REALLY Basic Torque Question

[Famah]

Greetings Learned Forum:

I need to torque my tractor's lug nuts. The rear rims are deep enough that I need to use an extension on my torque wrench. Way in the back of my mind, I have a memory from high school shop class (God bless you, Mr. Sveck) that adding an extension changes the torque actually being applied, as compared to the setting on the wrench. Is this true, or just the aftermath of too much partying after school? And if true, is there an easy way to account for the difference?

I greatly appreciate your thoughts and insights. Thank you.

Nick

 

[Monster5601]

I don't know for sure but I would assume that given a long extension, it would absorb some torque (or twisting action) but, how much I don't know. Then again, does it really matter in this case if your wheel lug nuts are +/- a few percent keeping in mind that torque wrenches are usually in the range of +/- 4% of accuracy?

My tractor specification calls for wheel torques in a range of (I forgot the actual numbers but something like) 145 to 160 foot pounds.

How to calculate what the extension would absorb would be tough because, for example, an extension designed for impact use is softer and would absorb more twisting. How would you be able to find this data for various extensions?

 

[J_J]

You might try these.

http://www.asedeals.com/video_accutorq_sockets.wmv

Amazon.com: Genius Tools Torque Extension Bar Set, 1/2-Inch Drive - 10 Piece: Home Improvement

http://www.torquestick.com/images/torque_chart.pdf

 

[Monster5601]

I have torque bars that I use with my impact tool (for cars) but, if you don't have an impact tool they have no value.

 

[Ductape]

I wouldn't worry about using an extension. I can't see how it would matter in your application.

I feel fortunate that I have a torque meter built into my elbow..... so I've never needed to own a torque wrench !

 

[mwb]

For every action there is an equal and opposite reaction. Using an extension between your wrench and a socket has no effect on the torque transmitted to the nut. Extensions on the square drive (including universal joints) will not change the "click point" of the wrench. Think of the socket and extension as a drive shaft - it can't create more or less torque if the force is transmitted axially.
The only way an extension can affect your torque is if it makes the the moment arm longer (like using a crows foot adapter).

If you are using an extension you will have to support the head of the wrench (no brainer here); the force you apply to the handle will want to make the wrench fall off. This also does not affect the torque applied.

Check here, under "torque facts" menu for some other info CDI Torque Products, America's Largest Manufacturer of Torque Equipment

 

[Famah]

Thanks mwb. I guess it was my parking lot exploits...

And I agree with the others that said it really doesn't matter for lug nuts. I was just curious. Thank you all for responding.

Nick

 

[RoyJackson]

Yes, you'll lose a bit of the torque value with an extention (or a crowsfoot,for that matter).
Do some research and you'll find a formula to factor in the extention.

However, I just add couple ft-lb's (or Nm's, if you into metric). One or two extra should do the job.

Just remember that torquing is not only to ensure the correct tightening of a fastener, it's to prevent overtightening, so don't go overboard on that torque value.

 

[rjmack]

don't forget the never-seize.

 

[Transit]

Nick, i can understand your concern, there are many ways to measure and set torque. Pro mechanics use impact wrenches because they are fast and powerful, too powerful in fact. So, to keep from over torquing the bolts they use torque rods to tame the guns.

The typical click type torque wrench is + - 3% accurate. There are wenches that set torque by angular displacement which are mostly for special applications.

If you set the torque to the midrange for the application you can't go wrong.

If you use a lubricant or anti seize compound than you must de-rate the torque. The easiest way to de-rate is to use the lower value in the range.

Lots of torque how-to sites to see if you wish.:thumbsup:

 

[mwb]

Yes, you'll lose a bit of the torque value with an extention (or a crowsfoot,for that matter).
Do some research and you'll find a formula to factor in the extention.

However, I just add couple ft-lb's (or Nm's, if you into metric). One or two extra should do the job.

Just remember that torquing is not only to ensure the correct tightening of a fastener, it's to prevent overtightening, so don't go overboard on that torque value.

Careful with this! An extension will not reduce your applied torque. A crowsfoot will amplify (increase) torque at the nut unless you put it on backwards (open end facing the wrench handle.

The OP was not asking about a crowsfoot I only added that to make sure it was not confused with a 'normal' straight extension. The link I posted gives you the formula for correcting for crowsfoot; there is no change when using a normal straight extension.

If you apply a torque to one end of a pipe (think drive shaft) the torque on the other end has to be the same (but in the opposite direction). It would not matter if your extension was 0.5 inches or 50 inches long. The fact that an extension may twist under load does not change the torque that is transmitted.

 

[RoyJackson]

Careful with this! An extension will not reduce your applied torque. A crowsfoot will amplify (increase) torque at the nut unless you put it on backwards (open end facing the wrench handle.

The OP was not asking about a crowsfoot I only added that to make sure it was not confused with a 'normal' straight extension. The link I posted gives you the formula for correcting for crowsfoot; there is no change when using a normal straight extension.

If you apply a torque to one end of a pipe (think drive shaft) the torque on the other end has to be the same (but in the opposite direction). It would not matter if your extension was 0.5 inches or 50 inches long. The fact that an extension may twist under load does not change the torque that is transmitted.

Problem with your comment is, although torque is transmitted, the typical micrometer setting ("Click" type) torque wrench will trigger prior to the transmission of torque through an extension. This is negligible, but in aerospace, we did have to factor for it.
I use a 1/2" drive micrometer setting torque wrench and I need a 6" 1/2" drive extension to torque my rear wheel bolts. That extension is pretty darn stiff (resistant to twist). As written earlier, I "guesstimate" about 2 ft-lbs of added torque to accomodate it (which is probably within the tolerance of the torque wrench anyway).
So, the illustration of a drive shaft isn't quite accurate (for a comparison to a torque wrench) because it doesn't account for the triggering of the wrench.

Now, we've added some real complexity to a "REALLY basic torque" question, haven't we?

 

[timswi]

Wow!!! Setting 2 on my impact seems to have the right torque for all wheels

I know you should torque them, but to be honest, I never have. I run them down on the second setting and double check them with a 4 way. Never cracked or warped a wheel (steel or aluminum) in my life.

 

[gpflepsen]

Problem with your comment is, although torque is transmitted, the typical micrometer setting ("Click" type) torque wrench will trigger prior to the transmission of torque through an extension. This is negligible, but in aerospace, we did have to factor for it.
I use a 1/2" drive micrometer setting torque wrench and I need a 6" 1/2" drive extension to torque my rear wheel bolts. That extension is pretty darn stiff (resistant to twist). As written earlier, I "guesstimate" about 2 ft-lbs of added torque to accomodate it (which is probably within the tolerance of the torque wrench anyway).
So, the illustration of a drive shaft isn't quite accurate (for a comparison to a torque wrench) because it doesn't account for the triggering of the wrench.

Now, we've added some real complexity to a "REALLY basic torque" question, haven't we?

With all due respect, I don't see this as being valid. Any torquing operation should be as "static" as you can make it to ensure good results. Every system of forces is going to be conservative, that is force in = force out, or in this case, torque in = torque out. A flexing drive extension is no different than pushing a spring to push a load. Force applied = force transmitted. Always

I'm all for learning something new, so if you can tell the whys of your position I'd appreciate it.

 

[banjodunn]

G'day i will throw my 2 cents in now, I have got three ext bars that i use in conjunction with a "click" type tension wrench and use these for engine building i have my wrench calibrated every twelve months, and i also send my bars down to get checked, 2"ext looses 1/2 ft/lb, 6" looses 1.2ft/lb and 12" looses 2.3 ft/lb. So i guess that they are prob accurate enough to use an ext but at least i can allow for it, as far as wheels go though i have never tensioned one in my 20+ years in the trade and never had a prob.


Jon

 

[SPYDERLK]

Problem with your comment is, although torque is transmitted, the typical micrometer setting ("Click" type) torque wrench will trigger prior to the transmission of torque through an extension. This is negligible, but in aerospace, we did have to factor for it.
I use a 1/2" drive micrometer setting torque wrench and I need a 6" 1/2" drive extension to torque my rear wheel bolts. That extension is pretty darn stiff (resistant to twist). As written earlier, I "guesstimate" about 2 ft-lbs of added torque to accomodate it (which is probably within the tolerance of the torque wrench anyway).
So, the illustration of a drive shaft isn't quite accurate (for a comparison to a torque wrench) because it doesn't account for the triggering of the wrench.

Now, we've added some real complexity to a "REALLY basic torque" question, haven't we?

Yeah! ... Incorrect stuff. Youre putting people who dont know any better into jeopardy. Get physic.
larry

 

[mjncad]

I have this little chart I got at McMaster-Carr and it's in the same drawer as my torque wrench.

Use this handy guide to reference torque requirements for inch nuts in 1/4" to 4" sizes and metric nuts in M4 to M100 sizes. The guide has 56 pages and measures 3 1/2" Wd. x 5 3/4" Ht.

Each90662A050$6.70

 

[c23380]

use to build engine for piston aircraft. Standard practice is that extentions do not change the torque much, IE not enough to worry about considering the +or- tolerances given in the manuals. this being said there is a shortcut when using crows feet or any other adapter the is not in line with the wrench. If you allign the adapter 90 degrees from the torque wrench direction of force then the setting on the scale will still fall well within the range of + or -. cylinders on Lycoming and Continental engines were all done this way for 30 to 40 years at our shop. Just passing this as it was passed to me by our Cheif engine builder.

 

[Transit]

use to build engine for piston aircraft. Standard practice is that extentions do not change the torque much, IE not enough to worry about considering the +or- tolerances given in the manuals. this being said there is a shortcut when using crows feet or any other adapter the is not in line with the wrench. If you allign the adapter 90 degrees from the torque wrench direction of force then the setting on the scale will still fall well within the range of + or -. cylinders on Lycoming and Continental engines were all done this way for 30 to 40 years at our shop. Just passing this as it was passed to me by our Cheif engine builder.

X2:thumbsup:

 

[RoyJackson]

use to build engine for piston aircraft. Standard practice is that extentions do not change the torque much, IE not enough to worry about considering the +or- tolerances given in the manuals. this being said there is a shortcut when using crows feet or any other adapter the is not in line with the wrench. If you allign the adapter 90 degrees from the torque wrench direction of force then the setting on the scale will still fall well within the range of + or -. cylinders on Lycoming and Continental engines were all done this way for 30 to 40 years at our shop. Just passing this as it was passed to me by our Cheif engine builder.

Yeah, pretty much negligible for short (6"), but we had to go by the manuals, so we used the calculations for correction. Of course, there was more then one occasion we did have to use longer (12+") extentions which, according to the Navy and aircraft manufacturers, did have an effect.